Bogen, Jim. "Theory and Observation in Science." STANFORD ENCYCLOPEDIA OF PHILOSOPHY January 6, 2009.

Scientists obtain a great deal of the evidence they use by observing natural and experimentally generated objects and effects. Much of the standard philosophical literature on this subject comes from 20th century logical positivists and empiricists, their followers, and critics who embraced their issues and accepted some of their assumptions even as they objected to specific views. Their discussions of observational evidence tend to focus on epistemological questions about its role in theory testing. This entry follows their lead even though observational evidence also plays important and philosophically interesting roles in other areas including scientific discovery and the application of scientific theories to practical problems. . . . Read the whole essay here: http://plato.stanford.edu/entries/science-theory-observation/.